1. Related Applications
This application relates to contemporaneously filed applications Ser. No. 09/548,922, entitled "Constant Displacement Oil Web System and Method of Operating the Same", and Ser. No. 09/548,924, entitled "Multi-Level Oiling Device and Process for a Fuser System", both of which are expressly incorporated herein by reference.
2. Field of the Invention
The present invention relates to an electrophotographic imaging apparatus, and more particularly to an oil web fuser oiling apparatus and a drive mechanism therefor.
3. Description of the Related Art
In a laser printer or similar apparatus using the electrophotographic process, an electrostatic image is created upon a photosensitive member, such as a roll or belt. Visible electroscopic marking particles, commonly referred to as toner, are applied to the electrostatic image on the photosensitive material. Thereafter, the toner is transferred to the desired media, which may include paper, transparency sheets or the like.
To make the toner image permanent on the media, the toner is fixed by the application of heat, frequently with the simultaneous application of pressure. The toner is elevated in temperature sufficiently to cause constituents of the toner to become tacky, and flow into the pores or interstices between fibers of the media. The simultaneous application of pressure can enhance the flow of the fluidized toner. Upon cooling, the toner again solidifies, causing the toner to adhere to the media.
Fixing the electroscopic toner images commonly has been accomplished by passing the media, with the toner image thereon, through a nip formed by opposed rolls, at least one of which is heated internally. The heated roll, referred to as a fuser roll, contacts the toner image, thereby heating the toner image as it passes through the nip. Under some operating conditions, the tackiness of the toner upon heating can cause the media to adhere to the fuser roll, and/or may cause a build up of toner on the fuser roll. By controlling the heat transfer to the toner, offset of toner to the fuser roll can be minimized. In a duplex imaging apparatus, wherein both sides of the media may be printed, toner offset, or media sticking problems may be enhanced. Further, toner may be transferred to the backing roll of the fuser roll couple, and transferred thereafter elsewhere in the apparatus. The presence of wayward toner particles in the imaging apparatus can degrade the quality of the printed sheets.
It is known in the electrophotographic process to reduce sticking, and toner offset to the fuser roll, by applying a release fluid to the surface of the fuser roll. The release fluid creates a weak boundary between the heated roll and the toner, thereby substantially minimizing the offset of toner to the fuser roll, which occurs when the cohesive forces in the toner mass are less than the adhesive forces between the toner and the fuser roll. Silicone oils having inherent temperature resistance and release properties suitable for the application are commonly used as release fluids. A known, available silicone oil that has been used advantageously in the past is polydimethylsiloxane.
A variety of fuser roll oiling systems have been used in the past, including oil wicking systems, oil delivery rolls and oil webs. Oil wicking systems include reservoir tanks of the desired release agent or oil, and a piece of fabric wick material having one end mounted in the reservoir and the other end spring biased against the hot roll. Oil from the reservoir is drawn through the fabric wick by capillary action, and is deposited against the roll surface. While a wicking system can be effective in supplying oil to the fuser roll, surface deposit of the oil on the roll can be inconsistent. and the replenishment or replacement of the oil and/or system can be difficult and messy.
An oil delivery roll system commonly includes an oil delivery roll nipped against the hot fuser roll, and either freely rotating against the fuser roll or driven against the roll through a gear train. Oil, delivered by various means to the surface of the oil delivery roll, is deposited on the hot fuser roll as the rolls rotate against each other. Various structures have been used for providing oil to the surface of the oil delivery roll, including reservoirs at the center of the roll providing oil to the roll surface through tubes or by means of capillary action in the outer material. Felts or metering membranes may be used in the oil delivery roll to control the oil flow through the roll. Another style of oil delivery roll, referred to as a web wrapped roll, includes high temperature paper or non-woven material saturated with oil, and wrapped around a metal core. In yet another type of oil delivery roll, a solid, oil secreting silicone rubber is used on the surface of the roll. The oil slowly secretes from the rubber and is deposited on the surface of the hot roll, without the need for a separate oil reservoir or metering layers.
Commonly used oil web systems include a supply spool of web material, generally being a fabric of one or more layers saturated with the desired oil. Non-woven fabrics of polyester and aramid fibers, such as Nomex.RTM. manufactured by DuPont, have been used satisfactorily in oil web systems in the past. A take-up spool is provided for receiving the used web. A web path, commonly including one or more guide rolls, extends from the supply spool to the take-up spool. A portion of the web path brings the web material into contact with the hot fuser roll, either by wrapping a portion of the web around the hot roll, or by utilizing a spring-loaded idler roll to nip the web material against the fuser roll. As the fuser roll rotates against the web in contact therewith, oil is transferred from the web to the fuser roll. Periodically, a drive mechanism for the take-up spool activates, rotating the spool and advancing web material from the supply spool to the take-up spool, thereby bringing a fresh section of web material into contact with the fuser roll.
Such conventional oil web systems can be used to deliver oil at a relatively constant rate with good uniformity. However, the oil flow is dependent on the amount of material brought into contact with the fuser roll over a given period of time. In conventional oil web systems, the simplified drive mechanisms for the take-up spool are attached to the fuser unit, or to the oil delivery apparatus, and have been operated for consistent durations at constant intervals throughout the life of the web system. Therefore, as spent material passes onto the take-up spool, and the diameter of the take-up spool increases, the length of web material brought into contact with the fuser roll increases during each web indexing procedure, thereby increasing the amount of oil deposited on the fuser roll.
Further, oil wicking systems, oil delivery rolls and oil web systems previously known in the art were designed only for a single oil delivery rate. By necessity, the delivery rate had to be for the maximum oil demand for the print processes to be performed and the media types to be used in the imaging apparatus. This often resulted in the over-application of oil under some conditions.
Improved oil web systems are described in co-pending patent applications entitled "Constant Displacement Oil Web System And Method For Operating The Same" and "Multi-Level Oiling Device And Process For A Fuser System", filed on even date herewith, and commonly assigned to Lexmark International, Inc. In the improved systems described in the aforementioned co-pending patent applications, an oil web device is disclosed in which the problem of the incremental increase in the linear advancement of the web as the take-up spool diameter increases has been solved by adjustment of the drive mechanism operating cycle. Further, the rate of oil application to the fuser roll can be varied dependent upon the media type being processed, and/or the desired glossiness of the printed image on the sheet. Media sticking and toner offset problems can be minimized without over-application of oil. Waste of the oil web system has been reduced substantially.
Drive mechanisms for oil web systems known in the past commonly have been mounted to the fuser unit or to the oil web unit; and, therefore, would be replaced when the respective unit to which it was attached would be replaced. Typically, the fuser unit and the oil web unit are considered to be replaceable units, each having a life expectancy less than the overall life expectancy of the base machine. Periodic replacement of each is necessary and expected. However, the drive mechanism for the oil web system can have a life expectancy equal to that of the base machine, and replacement may not be necessary during the expected machine life. Therefore, replacement of the drive mechanism with the fuser or oil web unit to which it is attached is wasteful and costly to the consumer.
Further, the drive mechanisms commonly used for oil web systems in the past did not provide precise control of the web advancement intervals, due to the coarse indexing control provided.
What is needed is an oiling device drive mechanism that is mounted in the base machine and is not replaced unnecessarily with units requiring periodic replacement. A further need is a multi-level oiling device drive mechanism having operating performance improvements for the more precise oil web systems currently available.